Lightning arrester



H. V. DRYER LIGHTNING ARRESTER Aug. ll, 1959 Filed Aug. l. 1956 lli - INVEN TOR.

Heng Z/'fyer Mem, @gte 2,399,587 Patented Aug. l1, 1959 LIGHTNINGARRESTER Henry V. Dryer, South Milwaukee, Wis., assignor toMcGraw-Edison Company, a corporation of Delaware Application August 1,1956, Serial No. 601,480

1 Claim. (Cl. 313-182) The present invention relates to lightningarresters for protecting electric power lines and equipment, and isparticularly directed to an improved spark gap assembly in combinationtherewith.

It has long been conventional practice to provide lightning arresters aspark gap assembly comprising a pile of spaced apart electrodes delininga plurality of series spark gaps. The electrode assembly is positionedto be in serial electrical arrangement with a valve element in the formof a non-linear resistance material, such as silicon carbide. Thesilicon carbide crystals may consist of individually molded blocksstacked in the arrester housing, or may be in the form of a solid massmolded directly to the housing, or, in certain cases, loose grain ispacked into the housing. In any case, the spark gap assembly isconventionally provided to work under atmospheric pressure, exceptperhaps, for an hermetic seal provided to maintain a moisture-proofatmosphere internally of the arrester housing.

It is also appreciated that the prior art contains various spark gapassemblies arranged in evacuated envelopes. However, nearly all of theheretofore presented embodiments were self-contained to function oncommunication or other relatively low power electric lines whereavailable power follow current was negligible when compared to currentavailable in power distribution or transmission circuits. Obviously, nocurrent limiting means was required for such purposes. In fact, inrecent years the development of the modern signal type arresters has ledaway from evacuated embodiments to relatively loose fitting housingsenveloping a simple set of gap electrodes with interposed ceramicinsulators.

It is also to be noted that a very recent contribution to the lightningprotection iield is disclosed as an evacuated spark gap assemblyintended for protection of high voltage lines. However, no means isprovided to limit available power follow current. A spark gap, no matterhow formed, when not provided with some means for limiting this current,is in itself limited in application by the available short-circuitcurrent. A spark gap assembly used alone is generally dependent uponback-up devices such as fuse cutouts or circuit breakers to handle powercurrent interruption.

In addition, a spark gap assembly, even when working properly tointerrupt follow current will add a momentary strain on all equipmentduring this abrupt action, unless such assembly is combined with a powerfollow current limiting means.

The present invention contemplates the provision of a lightning arresterspark gap assembly for use with a non-linear valve material, wherein atleast the spark gap assembly is maintained under evacuated conditions.Under such conditions, it has been observed that even in the case of asingle series gap, this gap will interrupt power follow currents of overthree times the magnitude of conventional arresters having as many as 13individual gaps defining a total air gap space of over 50 times the gapsetting dimension of the single evacuated gap.

It is, therefore, a primary object of the present invention to providean evacuated spark gap assembly for a lightning arrester.

Another object of the present invention is to provide a spark gapassembly for lightning arrester application, wherein said lightningarrester includes a non-linear valve element, and wherein at least thespark gap assembly is contained in an evacuated housing.

It is a further object of this invention to provide a single seriesspark gap in serial arrangement with a lightning arrester valve elementor other means for limiting follow current, and wherein at leastthespark gap portion is maintained under evacuated conditions.

Still another object of the present invention is to provide an improvedlightning arrester including a spark gap assembly of relatively shortlength and minimum number of parts, thereby materially reducingmanufacturing costs in fabrication andv assembly and further providing aunit ofcompact construction for ease in mounting with relation toequipment to be protected thereby.

A still'further-object of the presentv invention is to provide animprovedv lightning arrester including an evacuated spark gap assemblyincombination with-a nonlinear resistance valve element in which theinherent impedance of the arrester components regulates itself tocurrent flowing'and thereby provides not only follow-current limitation,but also adequate voltage limitation when high lightning 'currents liowAthrough the arrester.

Referring now to the drawing:

Fig.v l is a vertical elevational view, partly in section, of alightning arrester adopting yone embodiment of the present invention.

Fig. 2 is a vertical sectional view ofthe spark gap assembly portion,greatly enlarged, and removed from the housing.-

Fig. 3 is /a fragmentary sectional view of a portion of a spark gapassembly disclosing another embodiment of the present invention.

The embodiment of Figs. 1 and 2` of Athe present arrester comprises aspark' gap? assembly denoted generally by the reference numeral 1, andwhichmay be accommodated to alightning 'arresterofanyof the conventionaltypes. However, it'is shown herein as being enclosed in the chamber of aporcelain housing 2 which is provided with a series of axially spacedskirts or petticoats 3, and includes'conducting metal end caps 4 Iand 5.The porcelain housing 2 isl sealed at= each4 end by means of compressingand retaining av heavy resilient gasket 6 between the housing and aconducting -cap 7, which is spun in place over the'annular'flangeportion 8 of the housing while the assembly is under pressure in ahydraulic press. The endcaps are held in place adjacent the housing bymeans of a cement'9r poured between the end cap and the housing.

The electric line 10 to be protected by the lightning arrester isconnected to the conducting end cap 4 by means of-conventionalconnectors (not shown) received in an aperture in one of the integrallaterally projected ears 11. Connection with ground G may be made inlike manner with a projecting ear 12 of the conducting end cap 5.Contained within the housing 2 is a conventional valve material 15 ofsuitable quantity and generally comprising valve blocks or a solid massof negative resistance material, such as silicon carbide.

Although the spark gap-assembly 1 has been shown as being mounted atoneend of the lightning arrester, it is1wi'th'inthefprovince of the presentinvention to provide assemblies at either or at both ends thereof, or ininverted relationship'from the position shown, ifso desired.

In detail, the spark gap assembly lvof'the arrester ernbodimentdisclosed-inFigs. l and 2, comprises-a glass shell 20 with its externalsurface preferably being cor-v rugated, as shown, to provide an extendedcreepage and flashover distance between terminal connections. The glassshell is closed at its upper end as shown in Fig. 2, by means of acup-shaped terminal cap 21, which is formed with an annularinwardlydisposed ange 22 to provide stress relief as a means of minimizing theeffects of corona discharge. A conventional metal-to-glass seal isprovided between the shell 20 and the cap 21 with the aid of an annularring 23 externally of the shell and having a flanged margin contactingthe cap 21.

The lower end of the shell 20, as shown in Fig. 2, is also provided witha cup-shaped cap 24 also having an annular flange portion 22 extendingtowards the cap 21 to complete the relief of stresses occurring duringany corona discharge. The glass shell 20 also engages a conductingsleeve-like fitting 25 at its lower end, and is sealed thereto with aconventional metal-to-glass seal aided by the ring-like member 23. Inthe present case, the upper spark gap electrode 26 is stationarilysecured to the recessed portion 27 of the cap 21 and is in electricalContact therewith. It will be apparent from Fig. l that the cap 21 isconducting and electrically engages the spun cap 7 of the arrester tocomplete the circuit through the end cap 4 to line 10. The electrodemember 26 is preferably of tungsten, or may be of a steel rod having atungsten arcing portion 28 to provide a lesser expensive constructionthan of a rod composed entirely of tungsten.

The opposed or lower gap electrode 29 is preferably of similar materialas the electrode 26 and is adjustable as shown in the embodiment ofFigs. 1 and 2 and provides a variable spark gap 30 with the electrode26. The electrode 29 is axially slidable relative to the sleeve-likefitting 25, and is preferably threaded at the end to engage an adjustingstop nut 31, abutting the projecting fitting 25, for moving theelectrode in an axial direction to provide a predetermined gap setting.

The electrode 29 is provided with an hermetically sealed bellows 32,which is preferably of bronze, and terminates at one end in sealedrelationship with the sleeve-like fitting 25. The bellows permits axialmovement of the electrode 29 without breaking the vacuum within thechamber of the shell 20. The shell 20 is evacuated in the conventionalmanner to provide a very hard vacuum in the neighborhood of 0.1 micronof mercury, or as low as available high vacuum technique will provide.The bellows 32 is sealed at its upper end to a disk-like cap 33providing an air tight seal with the movable electrode 29.

The use of tungsten or similar high melting temperature and refractorymetals as the gap electrodes minimizes vaporization of the electrodesduring arcing. It is impossible, however, to prevent all vaporization ofelectrode metal. Without a baffle or barrier means of some kind, thevaporized metal condenses on the inside surface of the glass shell 20,and builds up thereon a conducting layer which eventually will developinto a short between the electrodes. This is prevented for the most partby surrounding the gap 30 with a member of vitreous material such as aglass baffle or shieldtube 35. The tube 1s supported by the shell at itsupper end and includes an aperture 36 at its lower end so as to providean extended leakage path between the electrodes. The tube 35 1s alsopreferably provided with an annular groove 37 for further constrictingthe member in the vicinity of the gap 30 .to act as a means ofaccelerating the dispersion of any arclng gases or metal vapor away fromthe gap.

As wlll be seen from Fig. 1, the assembly is mounted 1n serialarrangement with the valve element 15 and rests on a conducting plate40, being held in compressive relationship therewith by means of thecoiled spring 4I lnterposed' therebetween.A The spring 41 is preferablyshunted by a conducting flexible braid, or as shown, by means of aconducting exible strap 42. The Shllllf eliminates any problem ofintroducing any'illdlgtive reactance effects provided by a coiled springconductor under surge current conditions.

The second embodiment of the present invention is disclosed in detail inFig. 3, and provides a non-adjustable spark gap assembly for use inlightning arresters capable of being mass-produced at selected voltageratings. That is, in the embodiment of Figs. l and 2, the spark gapsetting 30 is adjustable by means of the nut 31 engaging the threadedportion of the axially movable electrode 29. Thus, factory adjustmentmay be made for a particular arrester from previously fabricated andstocked spark gap assemblies 1.

However, in the embodiment of Fig. 3, it will be apparent that thevarious components of the spark gap assembly are substantiallyidentical, except for the fact that the electrode 50 is statonarilysecured to the fitting 51 to provide a preselected and non-adjustablegap setting. Again the shield or tube 35 is provided and has a baliiefor condensing metal vapor which is adapt to lessen the ashover distanceof the shell 20. The shell 20 is sealed at its lower end to thecup-shaped cap 24 and is retained in place by the ring 23. Theconstruction is again evacuated to the greatest extent possible, whichat this time is in the neighborhood of about 0.1 micron of mercury.

As an illustration of the unexpected and successful operation of thearrester, various tests were conducted with a selection of gap spacings.Both 60-cyc1e and frontof-wave sparkover tests were run.

Tests conducted on the samples with the fixed gap setting in the rangeof approximately 0.01" to 0.1" indicated that even with a single highvacuum gap with a spacing of between 0.01 and 0.015", this gap couldreadily interrupt follow currents of over 400 amperes with 15 kv.applied 60cycle voltage. This is compared to a conventional arrester gapstructure employing 13 individual gaps with total air gap space ofapproximately 3A, which is only capable of interrupting follow currentson the order of 50 to 150 amperes at l5 kv.

Although the electrodes 26 and 29 and 50 have been illustrated in theirpreferred rod-like embodiment, it is within the Yscope of the presentinvention to provide them in any of many known forms such as plates ordisk-like members with supporting spacers (not shown). Other shellconfigurations and changes in operating components will also occur toone skilled in the art without departing from the broad aspects of thisinvention.

It will also be readily appreciated that it is within the scope of thisinvention to provide separate housing members, structurally independentof one another, but arranged for electrical connection with one another;one housing to contain the evacuated gap electrodes, while the otherwould contain the Valve element. Such construction would readily lenditself to providing an adjustable gap which may be stocked by amanufacturer for use with a variety of arrester valve housings, the gapto be adjusted for use with a certain size valve housing member.

It will be apparent that the present invention has provided an improvedlightning arrester of simplified and compact construction, which in itspreferred form, provides a single spark gap setting in an evacuatedatmos` phere and capable of interrupting power follow currents of muchhigher magnitude than conventional arresters having a plurality of gapstogether defining a relatively large total gap spacing.

I claim:

A lightning arrester for heavy duty power circuit use including anelongated housing of dielectric material, connector end caps cooperatingwith said housing to deiine a closed elongated chamber, a non-linearresistance valve element positioned in one end of said chamber, and aremovable spark gap unit positioned in the other end of said chamber,said unit including an evacuated envelope of dielectric material havingconducting terminal caps at opposite ends thereof, one of said terminalsbeing in electrical ponpection with a connecting end cap and the otherof said terminals being in electrical connection with said valveelement, a pair of opposed elongated spark gap electrodes eachrespectively in engagement with a conducting terminal cap, one of saidelectrodes being adjustably movable toward and away from the other tovary the dimension of the spark gap, an elongated vitreous shieldsurrounding said electrodes and said spark gap inside of said evacuatedenvelope, said shield being open at at least one end with the movableelectrode extending through said open end, means to adjust and x themovable electrode in a selected adjusted position, and an hermeticallysealed bellows in operable association with said adjusting means wherebysaid adjustable electrode may be moved while maintaining the evacuatedcondition of said envelope.

References Cited in the le of this patent UNITED STATES PATENTS

